This invention relates to coder and decoder devices for use in remotely controlling electrical equipment.
The present invention includes a decoder device for remotely controllable electrical equipment, the device comprising a receiver adapted to supply a predetermined output signal only when a predetermined access signal is applied to an input thereof, the access signal comprising two groups of pulsed electrical signals, each group comprising two pulses each of a predetermined frequency different from the other, an unlocking circuit, and means for applying the output signal from the receiver to the unlocking circuit, the unlocking circuit being switched to an enabled condition for a predetermined interval of time after receipt of a first of the said groups and providing the said predetermined output signal if a second of the said groups is then received in the said predetermined interval of time.
The invention also includes a coder device for generating signals for use in remotely controlling electrical equipment, the device comprising oscillator means adapted, when a coded input voltage is applied thereto, to generate an electrical signal or electrical signals of frequency determined by the coding of the input voltage, means for generating coded input voltages for the oscillator means, and means coupling the generating means to the oscillator means, the generating means being adapted, when operated, to generate a predetermined sequence of coded input voltages, whereby the oscillator means generate an access signal for rendering the electrical equipment accessible to subsequent control signals and comprising two groups of pulsed electrical signals, each group comprising two pulses each of a predetermined frequency different from the other.